The present invention relates to ovens with emissions controls, and more particularly to a baking oven having an integrated emissions control apparatus, i.e., emissions control apparatus which is intimately associated with and preferably incorporated directly into the baking oven for more efficient operation, energy and structural cost savings, and better control of emissions.
Industrial bakeries, principally those producing bread and buns, use a process of fermentation in order for the dough to rise and to insure the taste, texture and keeping qualities of the product. The fermentation produces alcohol as a byproduct. This alcohol is normally evaporated during the baking process, and is vented up the exhaust flues of the oven along with the moisture that is also driven off the dough during baking. Environmental studies have shown that alcohol is an ozone precursor, breaking down in the presence of sunlight to produce ozone and a series of other unstable and potentially hazardous chemical compounds. Environmental legislation is increasingly requiring the control of this type of emission, normally by its removal (i.e. condensation or biological breakdown) or destruction by intense heat. Current practice is to process the exhaust emissions through either a thermal incinerator operating in excess of 1400.degree. F. or a catalytic oxidizer running at lower temperatures around 700.degree. F. In both the thermal incinerator and the catalytic oxidizer, the alcohol and most other inorganic compounds that may be present are converted to carbon dioxide and water.
Devices to achieve this processing are typically large and heavy and require the construction of massive steel platforms or the like, which are typically located on the roof. Most roof installations require substantial reinforcements, which usually must be added to existing buildings, and so are relatively expensive and inconvenient. In addition, elongated and complex insulated ductwork with automatically operated dampers has to be built in order to connect such distain emissions control equipment with the oven, to allow the oven combustion safety equipment to function properly and to prevent premature condensation of water, alcohol or the vapors from the hot pan grease. Mishandling of the water, alcohol and vapors can cause corrosion as well as risk of fire.
Additionally, the cost of supplying the heat to raise the temperature of the exhaust gases from the baking temperatures of 350.degree.-400.degree. F. to either 700.degree. F. (for a catalytic oxidizer) or 1400.degree. F. (for a thermal incinerator) requires considerable amounts of fuel, adding to the costs of operating the bakeries. Although there are recuperation systems in use to reduce this fuel expense, the unsteady nature of the flow of alcohol in a working bakery puts practical limits on the efficiency of recuperation that can be employed. In addition, the extensive and complex ductwork and incinerator itself carries the long-term risk of cracking brought about by thermal expansion and contraction, which will give rise to leaking of the gases that must be controlled. This is either ignored or in better designed systems the fan moving the air in the oxidizers is positioned so that the "dirty" gas stream is under partial vacuum. The partial vacuum causes any leakage to be into the system rather than out of it. While effective, operating the fan at a partial vacuum increases considerably the size and power of the circulating fan required, thus increasing the electrical running costs of the unit.
Other industries, principally paint and printing industries have used systems which make use of exhaust gases with an inflammable content to fuel the heating of the ovens. These applications differ from the baking situation in that the stream of product is consistent, and it is practical to use the product as part of the primary heating. The alcohol in the bakery application is mixed with a very large amount of water vapor, which makes such use impractical for a number of the simpler recycling systems. Further, in the relatively closed atmosphere of a bakery oven the oxygen content of the atmosphere can easily be reduced seriously by repeated recycling, giving rise to combustion problems in the oven burners.
Thus, an apparatus solving the aforementioned problems is and has for quite some time been sorely needed in the baking art.